"The Sulfur Dance" Around Arenes and Heteroarenes ‐ the Reversible Nature of Nucleophilic Aromatic Substitutions

We disclose the features of a category of reversible nucleophilic aromatic substitutions in view of their significance and generality in dynamic aromatic chemistry. Exchange of sulfur components surrounding arenes and heteroarenes may occur at 25 °C, in a process that one may call a “sulfur dance”. These S_NAr systems present their own features, apart from common reversible reactions utilized in dynamic covalent chemistry (DCC). By varying conditions, covalent dynamics may operate to provide libraries of thiaarenes with some selectivity, or conversion of a hexa(thio)benzene asterisk into another one. The reversible nature of S_NAr is confirmed by three methods: a convergence of the products distribution in reversible S_NAr systems, a related product redistribution between two per(thio)benzenes by using a thiolate promoter, and from kinetic/thermodynamic data. A four‐component dynamic covalent system further illustrates the thermodynamically‐driven formation of a thiacalix[2]arene[2]pyrimidine by sulfur component exchanges. This work stimulates the implementation of reversible S_NAr in aromatic chemistry and in DCC.